Considerable prior art literature is available on the subject of spark ignition systems. Existing spark ignition systems for automobiles date back to about 1905. Although modern materials such as plastics and semiconductors have been used to improve the efficiency of the sparking coil, there has been little improvement to the basic principle, which provides for a 30 KV spark across two electrodes in the gasoline cylinder of the engine to ignite the fuel mixture. The single point ignition process effected by well known prior art spark plugs results in a slow moving flame-front across the engine cylinder. The speed of combustion resulting from this slow moving flame front necessitates advancing initiation of the spark as the engine speed increases, resulting in loss of power.
As is well known, diesel engines do not use spark plugs. Instead, fuel is injected into a preheated cylinder and is ignited by heat of compression. Similarly, high performance racing engines use glow plugs and doped alcohol fuels which tend to auto-ignite in a similar manner as the diesel principle, thereby achieving efficiency and performance significantly higher than spark ignition gasoline engines.
By the late 1970's, the effectiveness of plasma ignition systems was well accepted (L. A. Gussak (USSR), Energetikco Transport Academy Izvestijia (1965), Vol. No. 4, pp. 98-110 "New Principle of Ignition and Combustion in Engines"). However, as was also recognized at that time, the practical aspects of the application of plasma ignition systems to engines would require considerable further engineering research to qualify data on fuel economy, emissions and the LML (lean misfits limit).
Extensive research has been conducted in the characterization of plasma jet igniters, specifically at the lean misfire limit. The work of J. D. Dale at the University of Alberta, Edmonton, and A. K. Oppenheim at the University of California, Berkeley, and D. Fitzgerald at Jet Propulsion/CALTECH, stand out as the definitive and authoritative work leading to a true understanding of the application, benefits and superiority of plasma jet ignition over conventional spark ignition, for low-emission lean-burn engines. However, the practical implementation of such systems has been encumbered by severe hardware constraints and rapid electrode erosion, and as such, commercialization of such systems has not taken place.
Additional relevant prior art is disclosed in various issued patents.
U.S. Pat. No. 4,996,967 (Cummins Engine Company, Inc.) discloses an apparatus and method for generating a highly conductive channel for the flow of plasma current, in which a pre-pulse is utilized to ensure that an ionized channel is developed to a significantly conductive state prior to application of a current for sustaining of the plasma arc. However, according to the '967 Patent, the pre-pulse signal is in the form of a simple DC pulse. It has been found that the use of a single DC pulse may not always provide the best possible efficiency for ensuring complete ionization prior to onset of the plasma current.
U.S. Pat. No. 5,179,928 (Siemens Aktingeschellschaft) discloses means for generating an alternating current high voltage signal which is derived from a bipolar switcher with a tuned transformer section. The frequency of operation is adjusted when the spark plug operates in the plasma arc mode.
U.S. Pat. No. 4,998,526 (General Motors) discloses means for adjusting the plasma arc duration and magnitude of the plasma arc current in a fixed, non-adaptive manner. The arc current is maintained constant irrespective of the applied engine load.